1. Field of the Invention
The present invention relates to a sheet material supplying apparatus for feeding a sheet material such as a copying paper sheet, and relates more particularly to a sheet material supplying apparatus which includes an adsorbing unit for adsorbing a material to be adsorbed by a sucker and which is suitable for supplying an image forming material of an image recording apparatus onto which an image is to be formed by being transferred after development.
2. Description of Related Art
As an image recording apparatus, a structure is known in which a plurality of sheet materials cut into a predetermined size are accommodated in a laminated state in a sheet feeding tray and each one sheet is taken out of this tray for being supplied to an image forming section at the time when an image is formed.
The image recording apparatus of this type has a sheet feeding apparatus (a sheet material supplying apparatus) for supplying a plurality of sheet materials accommodated in the sheet feeding tray in a laminated state to a nip roller by taking out only the top layer sheet of the sheet materials from the tray by a friction between this sheet and a detaching roller rotating above the sheet materials.
However, in an image recording apparatus which is structured to transfer an image onto an image receiving material that is a sheet material after the image formed on a photo-sensitive material has been thermally developed, the image forming surface of the image receiving material is always wet and is easily adhered to other sheet when the sheets are laminated together because a coloring matter fixing material having a mordant is coated on the image forming surface of the image receiving material. Accordingly, there occurs a problem that not only the top layer sheet material but also a plurality of sheet materials reaching the lower layer are sent to the nip roller which results in a sheet feeding failure. Further, if the image recording apparatus is to be used in a high humidity atmosphere, the sheet materials come to be adhered to each other more easily.
Although it is possible to solve the sheet supplying failure by increasing the friction between the feeding roller and the image receiving material, the image forming surface is damaged by the friction between the feeding roller and the image receiving material when the image receiving material is to be accommodated in the sheet feeding tray by facing the image forming surface upward (that is, by facing the image forming surface to the feeding roller side).
Further, in the case of a sheet feeding apparatus for feeding a plurality of laminated sheet materials one by one from the top layer sheet, such as an image receiving material to be used for a thermal development and transfer or a sensitized sheet to be used for an X-ray photograph for medical purpose, for example, the use of a detaching roller like a sheet feeding apparatus that is used for a general copying machine or printer will cause a damage to the surface of the sheet materials by the friction between the sheet materials and the detaching roller. Therefore, a sheet feeding apparatus for feeding sheet materials by adsorbing the surface of the top layer sheet material is being used for the image receiving materials or the sensitized sheets.
In other words, the sheet feeding apparatus for the sheet materials of this type has a sucker disposed above the sheet materials. The sucker is brought into contact with the surface of the sheet material, then generates a negative pressure inside the sucker by a pump for evacuating air from inside the sucker by an elastic deformation of the sucker or through a hose or the like so that the sheet material is carried by being lifted in an adsorbed state. When the carrying of the sheet material is finished, the negative pressure inside the sucker is cancelled by sending air to the inside of the sucker by the pump through the hose or by releasing a valve connected to the sucker through the hose so that the adsorption of the sheet material is cancelled.
According to the sheet feeding apparatus of the above-described structure, however, the pump, the valve and the like are necessary in order to cancel the negative pressure within the sucker, and further, the hose is also necessary for connecting the pump and the valve with the sucker. Therefore, this arrangement becomes expensive and this also makes the overall apparatus complex. Furthermore, since a driving unit such as a motor for driving the sucker and the pump and the valve must be connected together in order to operate or release the pump and the valve at a predetermined carrying position, a control unit for this purpose becomes necessary. As a result, the overall apparatus becomes more complex and more expensive.